Hum balancer



1932- N. c. SCHELLENGER 1,335,633

HUM BALANCER Filed March 1. 1929 ll ll Ifiiillllllillrrmlllllli F NH/H In! 1 Patented a PATENT OFFICE NEWTON C. SCHELLENGER, OF ELKHART, INDIANA, ASSIGNOR TO CHICAGO TELEPHONE SUPPLY COMPANY, OF ELKIIART, INDIANA, A CORPORATION OF DELAWARE mm BALANCEB Application filed March 1, 1929. Serial No. 343,827.

My invention relates to hum balancers and has for its principal object the production of a new and improved hum balancer of simple compact design which can be cheaply manufactured. y

In radio circuits and the like in which the filament of a vacuum tube is lighted from raw alternating current, it is customary to balance outthe hum caused by the alternating current in the filament by a hum balancer to which the return circuit of the grid of the vacuum tube is connected.

A. hum balancer of this type usually comprises a fixed resistance of relatively high value which is connected directly across the filament of the tube, this connection usually being made as close to the tube socket as pos sible, A movable rider is adapted to sweep over this fixed resistance, and the grid return circuit of the tube is connected to this movable rider. Ii it is necessary to place a grid bias potential upon the grid of the tubes, suitable battery is inserted in the grid return lead ahead of the connection to the hum balancer. With the filament burning and the tubes functioning properly, an adjustment of the position of the rider on this fixed resist ance will ellectually balance out all of the hum produced by the alternating current in the filament After this has once been adjusted, there is little need for further adjustment as long as the tube and source of alternating current remain the same.

Heretofore, potentiometers have been employed as hum balancers. While these potentiometers successfully balance out. the hum, their use is objectionable for the reason that they are relatively large and therefore take up too much space in the radio set. Moreover, potentiometers are provided with knobsto permit their ready adjustment which knobs are necessary when the potentiometer is used for the purpose for which it was designed, but when used as a hum balancer the potentiometer knob is superfluous since after the initial adjustment has been made no further adjustment is necessary.

In the presentinvention I have provided a small compact hum balancer which is designed for use solely as a hum balancer and therefore of more simple design than a potentiometer. The balancer of the instant application is small enough that it does not take up an objectionably large amount of space in a radio set, and it can be cheaply In the drawing I have illustrated by way pf example a preferred embodiment oi: my lllVtEIllllOIllO acquaint those skilled in the art w1th the details of it,

Figure fl is a plan view or a completely assembled hum balanc r Figure 2 is an end view of the balancer shown in Figure 1,

Fi 3 i a portion or the circuit of a vacuum tube showing the hum balancer in m stalled.

referring to Figures 1 and 2, it will be seen that I have provided the insulating strip 1 around which is wound the resistance wire 2 to form the resistance unit of the hum balancer. Preferably the insulator strip 1 is made of a phenol condensation product such as bakelite, although either hard rubber or fiber might be used it desired. The opposite ends of the resistance wire 2 are wrapped 8 around the eyelets 3 and i and under the head thereof. These eyelets extend through holes in the insulator plate 1 and in the mounting plate 5 serving to secure the ends of the resistance wire 2 and also to mount the resistor unit upon the plate 5.

By using an eyelet such as 3 and 4 to fasten the ends of the resistance wire and to hold the two parts of the assembly together, I am able to employ this same fastening means to hold the wires connecting the resistance to the filament circuit. In connecting this hum balancer to the circuit, the wires are inserted in the eyelets 3 and 4 and soldered.

The mounting plate 5 which is also preferably made of a phenol condensation product such as bakelite, is secured by the hollow rivets 3, 4 in partially overlapping relation to the strip 1 and its resistance winding 2. The

turns of the resistance wire 2 are thus we clamped between the two plates 1 and 5 and are held against lateral displacement. The plate 5 carries the rider arm 6 which is pive otally mounted at the .center of, the plate 5 by the rivet 7. The free end of the rider 6 is bent downward to engage the resistance Wire under tension. The tension may be quite high since the turns of the coil 2 are firmly gripped by the twoplates 1 and 5 and are not easily displaced by the engagement of the end of the arm 6 or otherwise. The edge of the mounting plate 5 adjacent to the resistance wire 2 serves as a stop to limit the motion of the rider 6 across the res stance 2 so that in its extreme position the rider 6 does not break electrical engagement with the resistance wire.

An ear 14 is formed near the pivot point of the rider 6 to facilitate attaching the wire forming the electrical circuit to the rider.

vA slot-,8 is provided in the rider 6 through which slot a screw driver or other similar pointed instrument may be inserted to adjust the position of the rider upon the resistor. Since the plate 5 is disposed beneath the slot 8, there is no likelihood of the screw driver or other instrument injuring the resistance wire 6 during the adjusting operation. As may be seen from Figure '2 the central part of the rider or arm 6 is arched away from the surface of the plate 5. This serves a twofold purpose; first, it prevents the edges of the slot or of the arm from scraping along or scratching the surface of the plate, and also it allows the end of a screw driver to enter and obtain agood grip on the slot without slipping out and without scraping along the surface of the plate 5.

The mounting plate 5 is provided. with suitable holes near the outer end of the plate through which holes rivets, machine screws,

or eyelets are inserted to mount the hum balancer upon a suitable mounting support 9. The particular type of mounting su port will of course vary greatly in various a aptations of the invention. In some instances the mounting plate 9 will be a part of a metal sub-panel or base board of the radio set itself, and inother instances it may be a part of the tube socket containing the vacuum tube with which the hum balancer is designed to work. It is immaterial how the bracket is made so long as it is provided with suitable cars 12 which embrace the mounting holes and screws 10. The space between the ears 12 is left open so that if the mounting plate 9 be of metal there will be no likelihood of the rivet 7 coming in contact with that metal and disrupting the electrical circuit. Washers 11 a e used under the screw heads to guard against injury to the plate 5.

In Fig. 3, I have shown a vacuum tube 20 comprising the filament 21, the grid 22, and the plate 25. The filament 21 is heated by the transformer comprising primary likewise connected. The grid circuit of the' vacuum tube includes the grid 22, inductance 23, to ground at 23, with a' branch circuit through resistance 24, to the 'rider 6,- the circuit being connected to the car 14 by the flexible wire 16. In some circuits this rider might be connected through a grid biasing battery to the inductance 23 and be insulated from ground as is well understood. The transformer secondary 26 may also be used to supply the filament current for other vacuum tubes, not shown, such connections being indicated at 29 and 30.

With the primary winding 28 energized on alternating current, there is induced in the secondary winding 26 a voltage which drives current through the resistance 27 and through the hum balancer resistor 2 and the filament 21 in parallel.

By inserting suitable receiving devices, not shown, in the circuit of plate 25, the rider arm can be adjusted until the hum of the alternating current in the filament 21 disappears. To make this adjustment a screw driver or other similar pointed tool is in-' sorted in the slot 8 and the rider moved to the right 'or left until the balance point is located. When once this point is located, there is no further need of adjusting this hum balancer as the circuit conditions will remain the same and the hum will be balaneed out thereby...

While I have chosen to show a preferred embodiment of my invention by way of example, I am not to be limited by the specific details shown as there are many modifications and adaptations which can be made by one skilled in the art without departing from the scope of my invention.

Having thus complied with the the statutes and shown and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Patent as pointed out in the appended claims:

What is claimed is:

1. A rheostat comprising a flat strip of insulation having a resistance wire wound upon the central part thereof, a second fiat strip of insulation substantially parallel to the first strip and partially overlapping the same and holding the wire winding against lateral displacement, terminal means for the ends of the wire passing through the overtill lapping portions of both strips and holding them together, the portion of the second strip which does not overlap the first strip bearing a pivot pin and a contact arm having a flat hub held flat against the surface of the second strip by the pivot pin and having a contact making-end portion bent toward the first strip and engaging the turns of the winding,

2. A rheostat comprising a insulation having a resistance wire wound upon the central part thereof, a second flat strip of insulation substantially parallel to the first strip and partially overlapping the same and holding the wire winding against lateral displacement, terminal means for the ends of the wire passing through the ends of the overlapping portions of both strips and holding them together, said terminal means comprising hollow metal eyelets, the portion of the second'strip which does not overlap the first strip bearing a pivot pin, and a thin metal contact arm having a fiat hub held fiat against the surface of the sec ond strip by the pivot pin and having a contact making end portion bent toward the first strip and being adapted to engage the turns of the Winding, the travel of said arm angularly being limited by engagement with the edge of the second strip, said arm having a centrally arched portion bearing a slot for receiving a screwdriver to swing the arm about the pivot pin 3 lln combination for use with a mount" ing member having a pair of spaced perforated cars, a fiat strip of insulation having part of its width overlapping said care; said part having openings registering with the perforations in the cars, a second fiat strip of insulation having a coil of resistance wire about its central portion, said second strip and its coil of Wire being partly overlapped by part of the first strip, terminal pins securing the two overlapping parts of the strips together and serving as terminals for the winding on the second strip, a sheet metal contact arm having a flat hub member bearinn: against the surface of and pivoted upon said first strip and having a laterally deiiected central portion extending clear of the surface of both strips and having an end portion extending into engagement with the coils on the second strip, said end portion being limited in its angular movement by the edges of the first strip said hub having an integral terminal ear ior attachment of a conductor In witness whereof, I hereunto subscribe my name this 25th day of February, 1929.

NEWTON C SCHELLENGER.

flat strip of 

